There is great interest in the introduction of low-k dielectric materials into semiconductor devices. The use of insulating layers made of low-k dielectrics is expected to decrease the interconnect delay time, also called the RC delay, as semiconductor device geometries continue to shrink. Employing low-k dielectrics having suitable adhesion to the underlying conductive (e.g., copper) structures, however, has been problematic.
To reduce or alleviate the low-k dielectric adhesion problems, the industry places an adhesion layer, such as a silicon carbide nitride layer between the low-k dielectric layer and the underlying conductive structures. While the silicon carbide nitride adhesion layer helps, it does not completely eliminate all adhesion issues. For this reason, the industry treats the upper surface of the conductive structures with ammonia prior to forming the silicon carbide nitride adhesion layer. Fortunately, the ammonia treatment substantially eliminates the adhesion issues.
While the ammonia treatment substantially eliminates the adhesion issues, it introduces resist poisoning issues into the manufacturing process. Resist poisoning refers to the movement of contaminating materials present in various layers of the device into the resist. The resist is considered poisoned because the contaminating materials alter the reactive properties of the resist. In the instance of the ammonia treatment, the basic ammonia neutralizes the acids required to pattern the resist. Resist poisoning, in turn, can cause non-uniformities in the pattern, resulting in an imperfect transfer of the intended pattern into the substrate. This, in turn, limits the spatial resolution of device circuit features that can be achieved without a substantial increase in device defects.
In addition to the ammonia treatment of the upper surface of the conductive structures causing resist poisoning, the deposition process used to form a via etch stop layer located on the conductive structures also introduces resist poisoning problems. For example, many via etch stop layers contain nitrogen, the nitrogen typically being introduced with ammonia. Unfortunately, the ammonia that remains within the via etch stop layers after their manufacture, causes similar resist poisoning issues as typically result from the ammonia treatment of the conductive structures.
Previous attempts to reduce resist poisoning, whether introduced by the ammonia treatment, via etch stop layer, or another process, are unsatisfactory. For instance, the introduction of a barrier layer into the device itself to prevent movement of the contaminating materials into the resist has had limited success. The introduction of the barrier layer increases the cost and complexity of device fabrication. In some instances, it is impractical to remove the barrier layer after the threat of resist poisoning has past. Moreover, the barrier layer can increase the capacitance of the device, thereby causing undesirable increases in the RC delay.
Accordingly, what is needed in the art is an improved method of manufacturing semiconductor devices that can benefit from the use of low-k dielectrics, while not suffering the deficiencies of previous approaches.